1. Field of the Invention
The present invention relates to a magneto-optic recording medium in which at least a first magnetic layer for recording information and a second magnetic layer are laminated on a substrate, a magneto-optic recording system for recording information on the magneto-optic recording medium, and a magneto-optic recording method using the magneto-recording medium.
2. Description of the Related Art
FIGS. 9A to 9E are conceptual drawings of the operation of recording and erasing information in a magneto-optic recording medium. A magneto-optic recording medium 4 is arranged such that a first magnetic layer 2 which exhibits vertical magnetic anisotropy and whose direction of magnetization is reversible is laminated on a substrate 1, and a second magnetic layer 3 which exhibits vertical magnetic anisotropy and is magnetized in one direction and whose direction of magnetization is irreversible under the same conditions as those of the first magnetic layer 2 is laminated on the first magnetic layer 2. The second magnetic layer 3 of the magneto-optic recording medium 4 shown in FIG. 9B is magnetized in an opposite direction to that of the substrate 1, i.e., in an upward direction. In addition, the second magnetic layer 3 of the magneto-optic recording medium 4 shown in FIG. 9D is magnetized in a direction toward the substrate 1, i.e., in a downward direction. Thus, in the magneto-optic recording medium 4 of this type, there are two types of the direction of magnetization of the second magnetic layer 3, i.e., one which is oriented toward the substrate, and the other which is oriented away from the substrate.
A description will now be given of the operation in a case where information is recorded or erased with respect to the magneto-optic recording medium 4 thus arranged.
First, in cases where information is recorded or erased with respect to the magneto-optic recording medium 4 whose direction of magnetization of the second magnetic layer 3 is oriented away from the substrate 1, as shown in FIG. 9B, by means of recording signals RD representing "1" and "0", as shown in FIG. 9A, the magneto-optic recording medium 4 is rotated, and a downwardly oriented external magnetic field +H which is indicated by a bold arrow and which is oriented in an opposite direction to the direction of magnetization of its second magnetic layer 3 is applied to the magneto-optic recording medium 4. During the time when the recording signal is "1", a light beam LB with high output P.sub.H in a projecting direction indicated by an outline arrow, as shown in FIG. 9C, is projected onto the first magnetic layer 2. Then, when the first magnetic layer 2 is heated by the light beam LB and reaches its Curie temperature, the direction of magnetization of the first magnetic layer 2 is reversed in the same direction as that of the external magnetic field +H, i.e., in the direction toward the substrate 1. When the light beam LB ceases to be projected due to the rotation of the magneto-optic recording medium 4, and the temperature of the first magnetic layer 2 drops, the first magnetic layer 2 remains magnetized in the direction toward the substrate 1, thereby recording information. In addition, during the time when the recording signal RD is "0", the light beam LB with low output P.sub.L is projected to the first magnetic layer 2, as shown in FIG. 9C. As a result, the coersive force of the first magnetic layer 2 declines, and the direction of magnetization of the first magnetic layer 2 is influenced by the second magnetic layer 3 and is reversed in the same direction as the direction of magnetization thereof, i.e., the first magnetic layer 2 is magnetized in the direction away from the substrate 1, thereby erasing the information.
Meanwhile, in cases where information is recorded on the magneto-optic recording medium 4 whose direction of magnetization of the second magnetic layer 3 is oriented toward the substrate 1, as shown in FIG. 9D, in the same way as described above by means of the recording signal RD shown in FIG. 9A, during the time when the recording signal RD is "1", the light beam LB with low output PL is projected onto the first magnetic layer 2. Then, the coersive force of the first magnetic layer 2 declines, and the direction of magnetization of the first magnetic layer 2 is reversed in the direction of magnetization of the second magnetic layer 3, i.e., is magnetized in the direction toward the substrate 1, thereby recording information. Meanwhile, during the time when the recording signal RD is "0", the light beam LB with high output P.sub.H is projected onto the first magnetic layer 2, as shown in FIG. 9E. As a result, the first magnetic layer 2 is heated and reaches its Curie temperature, and the direction of magnetization of the first magnetic layer 2 is reversed in the same direction as that of the external magnetic field -H, i.e., is magnetized in the direction away from the substrate 1, thereby erasing the information.
Namely, in cases where information is recorded on the magneto-optic recording medium 4, the power of the light beam LB must be set to high output P.sub.H or low output P.sub.L in correspondence with the direction of magnetization of the second magnetic layer 3.
However, with the above-described magneto-optic recording medium, there are cases where the direction of magnetization of the second magnetic layer differs depending on its manufacturer. If the direction of magnetization of the second magnetic layer thus differs, there is a drawback in that information cannot be recorded on the magneto-optic recording media unless magneto-optic recording systems suited for the respective directions of magnetization are used.
For that reason, in order to record information on the magneto-optic recording media irrespective of the manufacturers of the magneto-optic recording media, it is necessary to provide separate magneto-optic recording systems for coping with the directions of magnetization of the second magnetic layer, so that there has been the problem that the equipment costs become high.